1. Field of the Invention
The present invention relates to an internal gear pump employed in a combustion engine and including an externally toothed inner rotor and an internally toothed outer rotor that mesh with each other and rotate in unison with revolution of the combustion engine for circulating a lubricant oil.
2. Description of the Prior Art
As a means for circulating a lubricant oil, filled within an oil pan of the combustion engine, to lubricate various components such as a bearing employed in the engine, an internal gear pump is well known in the art. See, for example, the Japanese Utility Model Publication No. 7-24566. The internal gear pump disclosed in this patent document includes an inner rotor and an outer rotor that are accommodated within a pump housing formed integrally with a crankcase and have respective end faces covered by a cover plate used to close the pump housing. The inner rotor is drivingly coupled with a pump shaft extending through the cover plate. The pump shaft has a driven gear meshable with a crank gear. The cover plate is fixed to an open end face of the pump housing by means of a plurality of bolts to seal between the pump housing and the crankcase.
It has, however, been found that the prior art internal gear pump requires extra cover plate, bolts and sealing member for sealing off a gap between a through-hole defined in the cover plate and the pump shaft. Accordingly, not only does the number of component parts used increase, but also a complicated and time-consuming work is required to fix the cover plate, having the pump shaft rotatably extending therethrough, to the pump housing by means of the bolts and then to seal off a gap between the pump shaft and the through-hole of the cover plate.